1. Field of the Invention
Aspects of invention relate to a safety circuit and a battery pack using the same, and more particularly to a safety circuit that can interrupt a main electric current path in which an electric current being supplied to a load flows, and a battery pack using the same.
2. Description of the Prior Art
A secondary battery can be repeatedly recharged and reused, in contrast to a primary battery that can be charged and used only once. Accordingly, the secondary battery frequently has been used as a main power supply of portable electronic devices for communication, information processing, and reproducing audio/video. The secondary battery is super lightweight and environmentally-friendly, and has a long life, a high energy density, a high output voltage, and a low self-discharge rate. Accordingly, a great deal of attention recently has been focused on the secondary battery, and its development has rapidly progressed.
There are various types of secondary batteries, such as a nickel-hydrogen (Ni-MH) battery and a lithium ion battery, etc., that use different electrode active materials. There are various types of lithium ion batteries, such as a liquid electrolyte battery, a solid polymer electrolyte battery, and a gel phase electrolyte, etc., that use different kinds of electrolytes. Secondary batteries have various types of packages, such as a prismatic type package and a pouch type package, etc.
Typically, a plurality of rechargeable secondary batteries are assembled into a battery pack for use in portable electronic devices, such as a portable computer. A charging/discharging control circuit is provided in the battery pack to control charging/discharging of the battery pack. The charging/discharging control circuit opens or closes a charging/discharging path by turning on or off a switching element to charge or discharge the battery pack. If the switching element is not operated at the proper time during charging/discharging of the battery pack, the battery pack may overheat due to overcharging, or due to an overcurrent caused by an overload or an electrical short in the battery pack, which may cause the battery pack to explode. A safety circuit including a thermal fuse may be provided in the battery pack to prevent this from happening by opening the thermal fuse when overcharging or an overcurrent is detected. However, an RF signal transmitted from a radio set operated near the battery pack may cause the safety circuit to malfunction and prevent the thermal fuse from opening when it should open, or cause the thermal fuse to erroneously open when it should remain closed. If the thermal fuse is prevented from opening when it should open, the battery pack may overheat and possibly explode. If the thermal fuse erroneously opens when it should remain closed, a device powered by the battery pack can no longer be used, thereby inconveniencing a user of the device. If this happens, and the thermal fuse is resettable, the thermal fuse can be reset and the battery pack can continue to be used to power the device. However, if the thermal fuse is non-resettable, it cannot be reset, and the battery pack can no longer be used to power the device, and must be replaced, thereby inconveniencing the user and causing the user to incur the expense of replacing the battery pack, which may be substantial.